Hydraulic, pneumatic and other actuated cylinders generally including a piston and attached cylinder rod arranged to move axially in a cylinder housing or body, are increasingly used in applications where it is desired or required to know the incremental and/or absolute position of the cylinder rod or another member such as a related cylinder body along a path of movement of one and/or the other, "absolute" referring to positional information without reference to a base, home, or starting position. The path of movement can represent, for instance, movement of the cylinder rod relative to the cylinder body or other member; movement of the cylinder body or other member relative to the cylinder rod; or any combination of relative movement between the cylinder rod, cylinder body and/or other member.
Various known linear sensors and resolvers are used for making cylinder rod and like positional determinations. However, such known linear sensors and resolvers have been found to suffer from operational inaccuracies owing to severe environmental conditions, such as temperature and humidity. Also, physical damage to such sensors under rugged work conditions can shorten their expected life, particularly, when used in the heavy equipment industry.
Various encoding systems are also known, using both incremental codes and absolute codes, for determining the position of a wide variety of elements along a path of movement, including cylinder rods. Reference for instance, Lappalainen et al. U.S. Pat. No. 5,632,916 issued May 27, 1997 to Partek Cargotec Oy; Kilpinen et al. U.S. Pat. No. 5,539,993 issued Jul. 30, 1996 to the same assignee; Schmitt U.S. Pat. No. 4,701,615 issued Oct. 20, 1987 to Johannes Heidenbain GmbH; Kibrick U.S. Pat. No. 4,901,073 issued Feb. 13, 1990 to Regent of the University of California; Gipp et al. U.S. Pat. No. 4,633,224 issued Dec. 30, 1986 to Caterpillar Inc.; and Salmi et al. International Patent Publication WO95/01510.
Problems found with various of such above referenced encoding systems include a need for an incremental scale for determining absolute position and, in some instances, the need for both an incremental scale and an absolute scale, directional limitations, lack of precision, and the need for actual movement to make the positional determinations.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.